1. Field of the Invention
This invention relates to an image reading or scanning apparatus in which image data read by image reading means are displayed on display means such as a cathode ray tube (CRT).
2. Prior Art
As a conventional image reading apparatus, there is known a scanning apparatus whereby digital image data produced upon reading an image document by an image sensor such as a CCD are output by way of a digital interface, such as a GPIB. For outputting the read image in a visible form, such as by printing or a monitor display, it is necessary to provide a computer in the system, thereby increasing the overall system scale. On the other hand, response properties are rather poor because of time-consuming signal processing operations. For this reason, the image reading apparatus, such as the conventional scanner, is not suited to be used for presentation purposes in an exhibition fair or lecture meeting.
In a copending patent application, filed in the name of the present Assignee, there is proposed an image reading apparatus in which an image document is read for storage in an image memory and the stored contents are repeatedly read from the image memory in synchronism with horizontal and vertical scanning signals of video signals so as to be output as video signals for displaying a still image.
Meanwhile, on the occasion of presentations, for example, it is frequently desired that an oral illustration or the like be made while attention is directed to desired portions of the displayed image. However, since verbal explanation is insufficient to make an accurate indication of the desired portion, it has been desired to evolve an image reading apparatus capable of making visual indications of the desired image portions in some form or other.
On the other hand, in the image reading apparatus adapted for directly outputting video signals, it has been envisaged to set the capacity of the image memory so as to be larger than the display range and to shift the reading region from the image memory by way of a so-called scroll display. The scroll display is such a display in which a memory reading region RA corresponding to the display range on a display screen SC of a monitor receiver MD of FIG. 8 is moved vertically for vertically shifting the contents of the image displayed on the display screen SC of the monitor receiver MD, as shown in FIG. 7. In such case, if the memory reading region RA is moved in an upward direction Yu with respect to the image document GD stored in the image memory, the contents of the displayed image on the display screen SC of FIG. 6 are moved in a downward direction Y.sub.D by way of a scrolling down operation.
Assuming that the pointer marks, such as arrows, are displayed for indicating desired portions of the image, and that, to this end, the above mentioned pointer mark display signals are generated by a character generator or the like and superimposed as output display signals on image data read from the image memory, if only the display contents of the image read from the image memory are scrolled, the portion indicated by the pointer mark is undesirably shifted with respect to the contents of the displayed image. It is also not desirable that characters having positional pertinence to the image contents, such as trimming frames, be deviated from the correct relative position at the time of scrolling.